star of wonderTom Volk's Fungus of the Month for December 2003

This month's fungus is Astraeus hygrometricus, an earthstar.

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Astraeus hygrometricus opening when exposed to water-- total elapsed time about 5 minutes

Earthstar of wonder,
Earthstar of night,
Earthstar of royal beauty bright...

Astraeus Christmas tree

This month's fungus honors that famous "star in the east," which led the three wise men to the manger. However, as its name would imply, this month's star is confined to the earth, usually in dry sandy areas, forming mycorrhizal relationships with the roots of pines and other trees. It's fun to find one of these small earthstars, which are usually about 2 inches (5 cm) across, including the rays.

This earthstar is sometimes called the "barometer earthstar," because the pointed rays of the star react to the amount of water in the air. When it's very dry, the ray-shaped arms fold around the center puffball to protect it from predators and the elements. However as the rains begin, the different parts of the hygroscopic rays absorb water at different rates, causing them to unfold to expose the center puffball. The time lapse animation to the left (total elapsed real time 5 minutes!) is a good representation of what happens when it rains. (For a page without the animation, click here.) Additional raindrops fall on the puffball part and the spores are puffed out, much like what happens in Lycoperdon pyriforme, the pear shaped wolf-fart puffball. However there's more! In addition to merely exposing the puffball part, the rays curl and extend far enough to slightly raiese the puffball part a couple of centimeters into the air, thus increasing the chances that the spores will get caught in the stream of air and be scattered to a far-off location. This small distance doesn't seem like much, but studies have shown a significantly stronger air stream just a few cm away from any rough surface. Thus the rays of the Astraeus fruiting body are not only beautiful, but also perform a function important for the survival of the species in a couple of different ways.

In Greek mythology, Astraeus was one of the Titans, responsible for the stars and the ancient arts of astronomy and astrology. His name means "the starry one," and he was the father of the four winds: Boreas, Zephyrus, Eurus, and Notus. Their mother was Eos, goddess of the dawn. Astraeus and Eos also bore THE ASTRA PLANETOI, the gods of the five Wandering Stars or Planets. The Greeks did not know of the planets Uranus, Neptune or Pluto, which were not discovered until modern times. Along with Helios, the sun, and Selene, the moon, each of these five gods ruled over one of the days of the week.

Anyway, back to the mushrooms. Often one of the first questions I am asked by people is, "Is it edible?" Although it does not look very appetizing to me, there are some people who will try anything. Here's an interesting email I received a couple of months ago.

Sky, the Cavalier King Charles spaniel who ate Astraeus"Please help: my puppy ate some Astraeus hygrometricus

Hello, thank you for taking the time to read my email. My Cavalier King Charles puppy ate several earth stars also know as Astraeus hygrometricus. I have called poison control and they do not know anything on this fungi. I am trying to find out how toxic they are. Will she die of liver failure? Anything you can tell me would be so greatly appreciated.

Sincerely, Lisa Borges & Sky (very sick little puppy)"

I wrote back: "So far as I know Astraeus hygrometricus is not a deadly poisonous mushroom. If it has any toxins they are not well characterized. They are likely to cause gastrointestinal upset, especially if they were 'ripe.' Certainly they will not cause liver failure (like death angels can). Although I am not a doctor or veterinarian, I speculate that the sickness will pass.

Hope this helps. Good Luck"

Just this week I got more information from Lisa about Sky's poisoning from Lisa.

"This entire ordeal started when our Cavalier King Charles Spaniel decided to help herself to plants in our back yard. She came in from being outside and started vomiting up blood. She then proceeded to have bloody diarrhea. We rushed her to the emergency vet clinic about 30 minutes away. They came in and insisted she had Parvo. Well, 3 Parvo tests later they were all negative. She was so lethargic and a bit incoherent. Her blood levels were high for a toxic poisoning. They were not sure if she would make it through the night. They kept her overnight and gave her antibiotics and IV fluids.

When we returned home we found several chewed up Earth Stars. She continued with the bloody diarrhea through the night. The following morning we had to take her to our regular vet Dr. Sue Sundburg. They ran blood tests on her and they were still elevated. They continued to give her IV fluids and we were still not sure if she was going to make it. At that point I started looking on line for any and all information on earth stars. Thankfully I found you. I was so extremely grateful for your quick response. I had emailed several people and you were the only one that returned my email. I will never be able to thank you enough. You gave me so much hope that she was going to be ok. I felt this huge weight lifted off of my chest. Poison control had said that they had no information on the Earth Star and that they treat all fungi as if it were deadly. She then proceeded to tell me that in many cases people die of organ failure a few days after they have eaten the item. That was such a difficult thing to hear. Well, she continued to be on IV fluids, antibiotics and continued to have daily blood tests. It took her several weeks to fully recover. Thanks to the excellent vet care we received she has made a full recovery. Please feel free to edit this as needed I am sorry I was rushing to get this over to you. Thank you so very much and have a wonderful holiday"

So Sky seems to be ok after this incident. Although they don't look very appetizing to me, you never know what your dog will eat! ...or surprisingly what some people will eat!

GeasterThere is actually another genus of earthstars, Geaster. In fact, Geaster means earthstar. Astraeus used to be in the genus Geaster, but was separated out by Andrew P. Morgan (a high school biology teacher in Cincinnati) in the latter part of the 19th century because of some technical reasons. (If you're not interested in the technical reasons, you may skip over the rest of this paragraph-- although this will not be on the quiz, you'll be missing out on something interesting...). According to Morgan [1889; North American Fungi. The Gasteromycetes: 1. Journal of the Cincinnati Society of Natural History 11:141-149], Astraeus "has no open chambers and therefore no organized hymenium. the threads of the capillitium are long and much branched.. columella entirely lacking, spores much larger than any Geaster." Don't those seem like silly little things to separate out a genus? -- But in 21st Century molecular analysis, it turns out Morgan was right!

According to this paper, Toward a Global Phylogeny of the Boletales by Roy Halling, Manfred Binder, and David Hibbett, Astraeus and Geaster are not even in the same family. According to their analysis Astraues belongs in the order Boletales, along with the boletes, such as Boletus edulis and Gyroporus cyanescens. They place Astraeus in the suborder Sclerodermatineae, in its own family, the Astraeaceae, probably most closely related to the Sclerodermataceae (such as Scleroderma, the false puffballs). In turn these are both related to Gyroporus, Calostoma, and Pisolithus, the dog turd fungus. I suppose the moral of the story is that there is much to be learned from careful morphological observations, such as Morgan's. You may recall that Morgan also was right about splitting up Laetiporus sulphureus into a couple of different species, including Laetiporus cincinnatus.

Interestingly, according to the latest molecular analysis, Geaster is probably related to the false chanterelle Gomphus, the stinkhorns Phallus and Dictyophora, the coral fungus Ramaria and the cannonball fungus Sphaerobolus. However the morphological analysis of this "Gomphoid=Phalloid clade" is not well resolved. Thanks to David Hibbett for this information.

I hope you enjoyed learning something about earthstars. They're beautiful little fungi to find, and they're fun to play with as well as being helpful to their associated trees.

If you have anything to add, or if you have corrections, comments, or recommendations for future FotM's (or maybe you'd like to be co-author of a FotM?), please write to me at

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